Islands such as Hawaii have some of the highest retail electric tariffs, for example (31 cents per kilowatt hour) due to a dependency on diesel generation. Renewable energy is a viable option such as offshore wind, solar and biomass renewable resources.
An offshore wind farm could connect to existing 138 kV grid as an generator. There are limited or no sites for utility scale wind or solar power installations. A direct connection into the 138 KV HECO (Hawaiian Electric Company), system is less costly than an inter island VHDC (Very High Density Cable). An offshore gearless WTG (Wind Turbine Generator) can provide the energy. Concrete slip form technology can be applied utilized with tension leg platforms and gravity anchors.
Conventional platforms are constructed in shallow waters because medium to deep water wind farms to subject to casualties from the elements. Few if any are able to survive the loss of a tension leg. Catenary restrained types or floaters are subject to too much motion such that the well-being of the WTG is compromised. Construction of deep water units are currently dependent upon large construction areas near the wind farm shoreline site which defaces the shoreline. Currently no economical means of building and deploying gravity anchors are available for deep water platforms.
As set forth in U.S. Pat. No. 7,075,189 by Heronemus et al., which is incorporated by reference herein, the term ‘wind turbine’ encompasses the drive train, gearbox, and generator for embodiments that include these elements. The word ‘rotor’ refers to the external rotating parts of a wind turbine, namely blades and a hub. Issues regarding loads, materials, structural dynamics, aerodynamics, controls, and power conversion must be taken into consideration in the construction of a wind turbine. The following references provide guidance for wind turbine design, all of which are incorporated herein by reference:    Guidelines for Design of Wind Turbines, Det Norske Veritas, Copenhagen and Riso National Laboratory, Denmark, 2002.    Hau, E., Windturbines—Fundamentals, Technologies, Application, and Economics,    Springer Verlag, Berlin Heidelberg, 2000.    Eggleston, D., Stoddard, F., Wind Turbine Engineering Design, Van Nostrand Reinhold,    New York, 1987.    Burton, T., Sharpe, D., Jenkins, N., Bossanyi, E., Wind Energy Handbook, John Wiley & Sons, West Sussex England, 2001.    Gasch, R., Twele, J., Wind Power Plants—Fundamentals, Design, Construction, and Operation, Solarpraxis AG, Germany, 2002.    Freris, L., Wind Energy Conversion Systems, Prentice Hall International Ltd., London,    1990.
Off shore wind turbines have unique design considerations related to wave loading, dynamics that are different from onshore turbines, corrosion due to a salt-water environment, and other factors. As noted in the above patent special chapters on design of offshore wind turbines can be found in Chapter 13 of the above reference entitled Wind Power Plants—Fundamentals, Design, Construction, and Operation and Chapter 16.6 of the above reference entitled Windturbines—Fundamentals, Technologies, Application, and Economics. The design of wind turbine rotors for a wind ship differs from land-based wind turbines in that the load specification will be different because at the platform tilts backward and forward, the relative wind speed that each rotor encounter varies and this dependence of loads on rotor dynamics is a factor.